In order to trigger hardmode, I need to kill the Guide? What did he ever do to me?

Sounds like you're very new to the game.

And haven't experienced him constantly opening the doors for every monster that comes to visit during the night.

He doesn't do that anymore, but those who played when that was happening are more than happy to let him die to get better loot.

I have it on good authority that the guide is a child pornogropher, meth dealer, and even worse, he cut off the "Do not remove by penalty of law" tag on his mattress.

He deserves to die!

"You wanna make an omelet, you gotta break some eggs"